This invention relates to devices and methods for maintaining a blood vessel or like passageways in an open condition and, if desired, for delivering medication to the blood vessel or passageway walls.
Vascular medical treatment procedures are known to include, among other things, occluding a blood vessel by thrombogenic devices, and maintaining the blood vessels open by use of a stent. Stents typically used in the past have consisted of a stainless steel tube section which includes selectively positioned gaps or openings which enable the section to be expanded (with a typically shortening of the length), for example, by a balloon catheter, after the section is positioned at the desired location in the blood vessel.
Problems with the above prior art stent, among other things, are that the length changes when the tubular section is expanded (the length shortened), and the length of the stent is limited since the greater is the length, the more difficult it is to deliver the stent to a target location in the blood vessel. That is, the stent being rigid, does not navigate well in the blood vessel, especially around tight corners. Further, since the described stent cannot be very long, numerous stents must be used for a diffuse diseased blood vessel.
A stent design which alleviates some of the above problems is disclosed in U.S. Pat. Nos. 5,292,331 and 5,674,278. This stent is comprised of a wire formed in a zig-zag pattern which extends in an annular configuration and which is compressed for disposition in a blood vessel and then expanded by a balloon catheter outwardly to hold the vessel walls apart.
A problem with the above and other unitary stents is that in the course of delivering them to a desired location in a blood vessel, the stents may become separated from the carrier/placement device, typically a balloon catheter, and drift downstream in the blood vessel. This, of course, could give rise to a dangerous situation in which the stent became lodged at a branch, bend, or at a distal narrowing in the vessel, and thus inhibit the flow of blood, This may require surgical intervention to remove the errant stent.
Besides the vascular medical treatment of maintaining blood vessels in an open condition, there are numerous situations where application of medications to an affected area of a vessel wall may be beneficial, for example, in treating arterial sclerosis, aneurysms or other weakening of the vessel wall, occlusive lesions, etc. Application of such medications may be done systemically by injecting medication into the vessel and then allowing the blood to carry the medication to the affected area. The problem with this approach is that high dosages of medication are required to ensure that some small portion reaches the affected area, and the high dosage may be harmful to other organs or body parts.
Another approach to treating diseases of vessel walls is to place a block before and after the affected area and then inject medications into the portion of the vessel between the two blocks. The problem with this approach is that blood flow is stopped for a certain amount of time and this, in itself, is dangerous.
Still another prior art approach is to thread a catheter through the blood vessel to the affected area and then either supply the medication through the catheter to the affected area, or supply the medication through a needle which itself is threaded through the catheter, pierce the vessel wall with the needle, and then supply the medication (see U.S. Pat. No. 5,354,279). The problem with simply supplying the medication via the catheter is that much of the medication is carried away in the blood and may adversely affect other organs.
A further prior art approach to supplying medication to a vessel wall involves the use of an inflatable sleeve positioned adjacent the affected area, where the sleeve includes an annular cavity holding the medication. When the sleeve is inflated to expand outwardly, the medication held in the cavity is placed into contact with the vessel walls and released thereinto. The problem with this approach is that the blood vessel again is blocked for a time and thus a gradual therapeutic regimen is not possible.
The placement of the stent can itself be a source of disease, by irritating the vessel wall at the points of contact. Also, thrombus can form on the stent causing a potentially fatal situation. The ability to deliver or release drugs or anti-thrombotic agents could reduce these problems.